1. Field of the Invention
The present invention relates generally to a fuel supply control system for an internal combustion engine of an automotive vehicle. More specifically, the invention relates to a fuel supply control system which controls fuel delivery amount on the basis of an intake air pressure and an engine revolution speed. Further particularly, the invention relates to a fuel supply control which can perform precise and high response fuel delivery control with minimum memory capacity.
2. Description of the Background Art
In one of typical fuel supply control system, an intake air pressure and an engine revolution speed are taken as basic parameter for deriving a basic fuel supply amount. Usually, the basic fuel supply amount is derived by table look-up against a two-dimensional table in terms of the intake air pressure and the engine revolution speed. However, derivation of basic fuel supply amount requires more complex process because mixture volume efficiency which is efficiency in packing of air/fuel mixture into a combustion chamber. Furthermore, in order to obtain satisfactory precision in fuel supply amount control, relative large two-dimensional look-up table becomes necessary. This requires not only higher cost but also longer process time to cause lag in acceleration and deceleration to lower fuel control performance.
Because of long process period required in setting the basic fuel supply amount, table look-up operation is generally done in a background job. In such case, updating of the basic fuel supply amount versus the intake air pressure and the engine revolution speed cannot be updated frequent enough to maintain an air/fuel ratio in the vicinity of stoichiometric value in an engine driving condition which requires frequent interruption of the background job.
For improving the drawback in the conventional art set forth above, Japanese Patent First (unexamined) Publications (Tokkai) Showa 58-41230 and Showa 59-32634 propose use of one-dimensional maps which are separately set for separately looking up in terms of the intake air pressure and the engine revolution speed for deriving induction volume efficiency. The induction volume efficiency derived in terms of the intake air pressure is multiplied with that derived in terms of the engine speed. In the alternative approach, both two-dimensional map and one-dimensional maps are used so that the induction volume efficiency is derived utilizing the two-dimensional map while the engine is in low speed range and is derived utilizing the one-dimensional maps while the engine is in high speed range. However, in either case, the precision level in air/fuel ratio control cannot be satisfactorily high.